The common surface treatment methods of narrow-band copper sheet are introduced.

The surface treatment method of narrow-band copper sheet should be selected according to the requirements of corrosion resistance, conductivity and appearance decoration of the application scene. The common treatment methods and characteristics are as follows:

A, cleaning and protective treatment

Remove oil stains and oxides on the surface by physical or chemical methods, and at the same time form a protective layer to improve the basic performance.

Mechanical cleaning

Methods: Ultrasonic cleaning, drum polishing or electrolytic cleaning are used to remove surface grease, dust and slight oxide film.

Application: pretreatment of electronic components, basic cleaning before subsequent coating.

Features: fast and efficient, without changing the material thickness, suitable for precision narrow band.

Chemical cleaning (pickling)

Methods: Use dilute sulfuric acid, citric acid and other solutions to remove oxide scale (such as copper oxide), and then wash and dry after the reaction.

Application: surface activation of copper strip after rolling or cutting to prepare for coating.

Attention: The acid concentration and treatment time should be controlled to avoid the copper strip from thinning due to excessive corrosion.

anti-corrosive treatment

Oil/wax coating: the surface is coated with antirust oil (such as mineral oil and synthetic oil) or wax layer to isolate humid air.

Application: protection in long-term storage or transportation, often used for uncoated general narrow band.

Passivation treatment: a transparent passivation film is formed by chromate (such as trivalent chromium) or chromium-free passivator to improve corrosion resistance.

Application: scenes with low requirements for environmental protection in the fields of electronics and automobiles (it should be noted that some industries restrict chromium-containing processes).

Second, the coating treatment (metal coating)

By electroplating, electroless plating and other processes, a metal coating is deposited on the copper surface, giving it the characteristics of conductivity, corrosion resistance and wear resistance.

Tin plating (Sn)

Process: electroplating or hot dip plating, the thickness of the coating is usually 1 ~ 5 μ m.

Features:

Good electrical conductivity (resistivity about 11.5 μΩ・cm) and excellent weldability, used for electronic component pins and battery connecting plates.

The cost is low, but the corrosion resistance is general, and it is easy to be oxidized after long-term exposure (with antioxidant coating).

Environmental protection: environmental protection lead-free tin plating solution (in line with RoHS standards) is required.

Nickel plating (Ni)

Process: Electroplating or electroless nickel plating (such as electroless nickel plating) with a thickness of 2 ~ 10μ m..

Features:

High hardness (HV 200~500) and good wear resistance, used for connectors and springs that need wear resistance.

The corrosion resistance is better than that of copper, and it can be used as the bottom coating (such as gold/silver plating after nickel plating) to enhance the bonding force.

Note: the conductivity of nickel layer is slightly lower than that of copper (resistivity is about 6.8 μΩ・cm), so it is necessary to balance performance and cost.

Gold plating (Au)

Process: gold plating or electroless gold plating with a thickness of 0.1~3 μm (thin gold is used for electronics and thick gold is used for contacts).

Features:

Excellent conductivity (resistivity 2.4 μΩ・cm), strong oxidation resistance, never rusting, suitable for high-frequency communication and precision instrument contacts.

High cost, often used in high-end scenes (such as aerospace, medical equipment).

Silver plating (Ag)

Process: silver electroplating with a thickness of 0.5~5 μm m.

Features:

The highest conductivity (resistivity 1.6 μΩ・cm), superior to copper and gold, is used for high-frequency signal transmission (such as RF components).

It is easy to oxidize to produce black silver sulfide (Ag₂S), which needs anti-tarnishing treatment (such as coating organic film).

Copper plating (Cu)

Process: Electroplating copper (acid copper plating or cyanide copper plating) with a thickness of 5 ~ 20μ m..

Features:

As the bottom coating, it can enhance the adhesion of subsequent coatings (such as nickel and chromium) or be used to repair the surface defects of copper strip.

The cost is low, but the corrosion resistance is not significantly improved, and it is often used as the intermediate layer of multilayer coating.

Third, functional coating treatment

Improve the surface performance by organic or inorganic coating to meet the requirements of specific scenes.

Anti-oxidation coating (anti-discoloration treatment)

Methods: Chemical agents such as organosilane and benzotriazole (BTA) were coated to form a molecular protective film.

Application: Long-term storage or exposed scenes of uncoated bare copper strip (such as architectural decoration and hardware).

Features: transparent and colorless, does not affect the conductivity of copper strip, and the environmentally friendly formula can pass RoHS certification.

Insulating coating

Mode: coating insulating paint such as epoxy resin and polyimide (PI) with a thickness of 10 ~ 50μ m..

Application: Used for copper tape that needs insulation (such as motor winding and transformer coil).

Features: Withstand voltage up to several thousand volts, oil resistance and heat resistance at the same time (the temperature resistance of some coatings is above 200℃).

lubricant coating

Mode: coating graphite, molybdenum disulfide (MoS₂) or polymer lubricant.

Application: copper strip that needs subsequent stamping and drawing to reduce die wear and material cracking.

Features: It can be cleaned and removed after processing, or retained as a functional coating (such as self-lubricating parts).

Fourth, surface modification treatment

Change the surface structure by physical or chemical methods to improve the material properties.

anodize

Principle: Copper strip is used as anode to form oxide film (mainly copper oxide CuO or cuprous oxide CuO) in electrolyte.

Application: Less used for pure copper, more used for copper alloy (such as brass), forming decorative oxide film (such as bronze color) or enhancing corrosion resistance.

Limitations: the oxide film is thin (usually < 1 μm) and the wear resistance is limited.

Heat treatment modification

Methods: Work hardening is eliminated by annealing (such as bright annealing), and the surface finish is improved (such as mirror effect).

Application: Surface optimization of high-precision narrow band (such as optical components and electronic shielding materials).

V. Selection suggestions

Conductivity is preferred: silver plating and gold plating are preferred, followed by bare copper (which needs anti-oxidation treatment).

Corrosion resistance is preferred: nickel plating+chromium plating (such as bathroom hardware), passivation treatment or organic anti-oxidation coating.

Welding priority: tin plating and silver plating (with flux).

Environmental protection requirements: the European Union and other markets need to choose lead-free and chromium-free processes (such as chromium-free passivation and environmentally friendly tin plating).

Note: Surface treatment may affect the thickness (such as coating thickness) and tolerance of copper strip, and it should be clearly requested with the manufacturer when customizing to avoid affecting subsequent assembly or function.